/*
 * Copyright 2001-2005 (C) MetaStuff, Ltd. All Rights Reserved.
 *
 * This software is open source.
 * See the bottom of this file for the licence.
 */

package org.dom4j.tree;

import java.lang.ref.WeakReference;
import java.lang.reflect.Constructor;
import java.util.Map;

import org.dom4j.Namespace;

/**
 * <p> <code>NamespaceCache</code> caches instances of
 * <code>DefaultNamespace</code> for reuse both across documents and within
 * documents. </p>
 * 
 * @author <a href="mailto:james.strachan@metastuff.com">James Strachan </a>
 * @author Maarten Coene
 * @author Brett Finnell
 * @version $Revision: 1.2 $
 */
public class NamespaceCache
{
   private static final String CONCURRENTREADERHASHMAP_CLASS =
      "EDU.oswego.cs.dl.util.concurrent.ConcurrentReaderHashMap";

   /**
    * Cache of {@link Map}instances indexed by URI which contain caches of
    * {@link Namespace}for each prefix
    */
   protected static Map cache;

   /**
    * Cache of {@link Namespace}instances indexed by URI for default namespaces
    * with no prefixes
    */
   protected static Map noPrefixCache;

   static
   {
      /* Try the java.util.concurrent.ConcurrentHashMap first. */
      try
      {
         Class clazz = Class.forName("java.util.concurrent.ConcurrentHashMap");
         Constructor construct = clazz.getConstructor(new Class[]
         { Integer.TYPE, Float.TYPE, Integer.TYPE });
         cache = (Map) construct.newInstance(new Object[]
         { new Integer(11), new Float(0.75f), new Integer(1) });
         noPrefixCache = (Map) construct.newInstance(new Object[]
         { new Integer(11), new Float(0.75f), new Integer(1) });
      }
      catch(Throwable t1)
      {
         /* Try to use the util.concurrent library (if in classpath) */
         try
         {
            Class clazz = Class.forName(CONCURRENTREADERHASHMAP_CLASS);
            cache = (Map) clazz.newInstance();
            noPrefixCache = (Map) clazz.newInstance();
         }
         catch(Throwable t2)
         {
            /* If previous implementations fail, use internal one */
            cache = new ConcurrentReaderHashMap();
            noPrefixCache = new ConcurrentReaderHashMap();
         }
      }
   }

   /**
    * DOCUMENT ME!
    * 
    * @param prefix DOCUMENT ME!
    * @param uri DOCUMENT ME!
    * 
    * @return the namespace for the given prefix and uri
    */
   public Namespace get(String prefix, String uri)
   {
      Map uriCache = getURICache(uri);
      WeakReference ref = (WeakReference) uriCache.get(prefix);
      Namespace answer = null;

      if(ref != null)
      {
         answer = (Namespace) ref.get();
      }

      if(answer == null)
      {
         synchronized(uriCache)
         {
            ref = (WeakReference) uriCache.get(prefix);

            if(ref != null)
            {
               answer = (Namespace) ref.get();
            }

            if(answer == null)
            {
               answer = createNamespace(prefix, uri);
               uriCache.put(prefix, new WeakReference(answer));
            }
         }
      }

      return answer;
   }

   /**
    * DOCUMENT ME!
    * 
    * @param uri DOCUMENT ME!
    * 
    * @return the name model for the given name and namepsace
    */
   public Namespace get(String uri)
   {
      WeakReference ref = (WeakReference) noPrefixCache.get(uri);
      Namespace answer = null;

      if(ref != null)
      {
         answer = (Namespace) ref.get();
      }

      if(answer == null)
      {
         synchronized(noPrefixCache)
         {
            ref = (WeakReference) noPrefixCache.get(uri);

            if(ref != null)
            {
               answer = (Namespace) ref.get();
            }

            if(answer == null)
            {
               answer = createNamespace("", uri);
               noPrefixCache.put(uri, new WeakReference(answer));
            }
         }
      }

      return answer;
   }

   /**
    * DOCUMENT ME!
    * 
    * @param uri DOCUMENT ME!
    * 
    * @return the cache for the given namespace URI. If one does not currently
    *         exist it is created.
    */
   protected Map getURICache(String uri)
   {
      Map answer = (Map) cache.get(uri);

      if(answer == null)
      {
         synchronized(cache)
         {
            answer = (Map) cache.get(uri);

            if(answer == null)
            {
               answer = new ConcurrentReaderHashMap();
               cache.put(uri, answer);
            }
         }
      }

      return answer;
   }

   /**
    * A factory method to create {@link Namespace}instance
    * 
    * @param prefix DOCUMENT ME!
    * @param uri DOCUMENT ME!
    * 
    * @return a newly created {@link Namespace}instance.
    */
   protected Namespace createNamespace(String prefix, String uri)
   {
      return new Namespace(prefix, uri);
   }
}

/*
 * Redistribution and use of this software and associated documentation
 * ("Software"), with or without modification, are permitted provided that the
 * following conditions are met:
 * 
 * 1. Redistributions of source code must retain copyright statements and
 * notices. Redistributions must also contain a copy of this document.
 * 
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 * 
 * 3. The name "DOM4J" must not be used to endorse or promote products derived
 * from this Software without prior written permission of MetaStuff, Ltd. For
 * written permission, please contact dom4j-info@metastuff.com.
 * 
 * 4. Products derived from this Software may not be called "DOM4J" nor may
 * "DOM4J" appear in their names without prior written permission of MetaStuff,
 * Ltd. DOM4J is a registered trademark of MetaStuff, Ltd.
 * 
 * 5. Due credit should be given to the DOM4J Project - http://www.dom4j.org
 * 
 * THIS SOFTWARE IS PROVIDED BY METASTUFF, LTD. AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL METASTUFF, LTD. OR ITS CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * 
 * Copyright 2001-2005 (C) MetaStuff, Ltd. All Rights Reserved.
 */
